On Sat, 3 Mar 2012, Anton Vorontsov wrote: > si_meminfo() calls nr_blockdev_pages() that grabs bdev_lock, but it is > not safe to grab the lock from the hardirq context (the lock is never > taken with an _irqsave variant in block_dev.c). When taken from an > inappropriate context it easily causes the following deadlock: > > - - - - > ================================= > [ INFO: inconsistent lock state ] > 3.2.0+ #1 > --------------------------------- > inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage. > swapper/0/0 [HC1[1]:SC0[0]:HE0:SE1] takes: > (bdev_lock){?.+...}, at: [<ffffffff810f1017>] nr_blockdev_pages+0x17/0x70 > {HARDIRQ-ON-W} state was registered at: > [<ffffffff81061b20>] mark_irqflags+0x140/0x1b0 > [<ffffffff81062f03>] __lock_acquire+0x4c3/0x9c0 > [<ffffffff810639c6>] lock_acquire+0x96/0xc0 > [<ffffffff8131c58c>] _raw_spin_lock+0x2c/0x40 > [<ffffffff810f1017>] nr_blockdev_pages+0x17/0x70 > [<ffffffff81089ba8>] si_meminfo+0x38/0x60 > [<ffffffff81675493>] eventpoll_init+0x11/0xa1 > [<ffffffff8165eb40>] do_one_initcall+0x7a/0x12e > [<ffffffff8165ec8e>] kernel_init+0x9a/0x114 > [<ffffffff8131e934>] kernel_thread_helper+0x4/0x10 > irq event stamp: 135250 > hardirqs last enabled at (135247): [<ffffffff81009897>] default_idle+0x27/0x50 > hardirqs last disabled at (135248): [<ffffffff8131e1ab>] apic_timer_interrupt+0x6b/0x80 > softirqs last enabled at (135250): [<ffffffff8103814e>] _local_bh_enable+0xe/0x10 > softirqs last disabled at (135249): [<ffffffff81038665>] irq_enter+0x65/0x80 > > other info that might help us debug this: > Possible unsafe locking scenario: > > CPU0 > ---- > lock(bdev_lock); > <Interrupt> > lock(bdev_lock); > > *** DEADLOCK *** > > no locks held by swapper/0/0. > - - - - > > The patch fixes the issue by using totalram_pages instead of > si_meminfo(). > > p.s. > Note that VMEVENT_EATTR_NR_SWAP_PAGES type calls si_swapinfo(), which > has a very similar problem. But there is no easy way to fix it. > > Do we have any use case for the VMEVENT_EATTR_NR_SWAP_PAGES event? If > not, I'd vote for removing it and thus keeping things simple. > > Otherwise we would have two options: > > 1. Modify swap accounting for vmevent (either start grabbing > _irqsave variant of swapfile.c's swap_lock, or try to > make the accounting atomic); > 2. Start using kthreads for vmevent_sample(). > > Signed-off-by: Anton Vorontsov <anton.vorontsov@xxxxxxxxxx> Applied, thanks! -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>